1. Field of the Invention
The present invention relates to liquid phase, acid catalyzed alkylation of isoparaffin hydrocarbon with olefin hydrocarbon for production of alkylate having high octane value and being suitable for gasoline blending stock. More particularly, the present invention relates to such an alkylation process wherein improved acid catalysts comprising selected ratios of fluorosulfonic and sulfuric acid are employed.
2. Description of the Prior Art
Liquid phase alkylation processes wherein isoparaffin hydrocarbons, such as isobutane, isopentane, etc. are alkylated with olefin hydrocarbons such as propylene, butylenes, etc., for production of alkylate products comprising highly branched C.sub.7 -C.sub.8 range paraffin hydrocarbons having high octane values, are well known and widely practiced. In such alkylation processes, reactant hydrocarbons are generally contacted in the liquid phase, at temperatures in the range of from about 0.degree. F-100.degree. F, in the presence of acid alkylation catalyst under conditions of good mixing to produce the desired alkylate hydrocarbons. Reaction pressures, which may vary from about ambient to superatmospheric, are sufficient to maintain reactants in the liquid phase. Higher pressures apparently have no substantial effect upon such alkylation reactions. Acid catalysts may be selected from a wide range of strong acids including sulfuric acid and fluorosulfonic acid. Generally, liquid alkylation catalysts such as sulfuric acid and fluorosulfonic acid are substantially immiscible with isoparaffin hydrocarbon reactants. Consequently, reactant hydrocarbons and liquid alkylation catalysts are contacted in an alkylation zone under conditions of high shear mixing sufficient to form an emulsion of immiscible hydrocarbon and catalyst. Detailed description of such alkylation processes is not required herein, as such processes are well known and widely practiced in the prior art.
In such alkylation processes side reactions take place in addition to desired alkylation reactions wherein 1:1 olefin-isoparaffin adducts are produced. For example, olefin hydrocarbons tend to polymerize in the presence of strong acid catalysts to form C.sub.12 and higher molecular weight polymers; also such polymers tend to crack in the presence of the strong acid catalyst forming low octane C.sub.5 -C.sub.7 hydrocarbons. These side reaction products, e.g., olefin polymers and cracked products, have relatively low octane values and are not as desirable as the 1:1 olefin isoparaffin alkylation products for use as gasoline blending stocks.
In order to maximize the yield of the desired alkylate products at the expense of the undesired side reaction products, care is taken to insure good contact of isoparaffin reactants with olefin reactants in the presence of alkylation catalysts under reaction conditions which favor formation of alkylate hydrocarbon products over side reaction products. For example, reaction temperatures are maintained in the range of about 0.degree. F to about 100.degree. F wherein the alkylation of isoparaffins with olefins proceeds at economically attractive rates and wherein olefin polymerization rates are not so great as to consume excessive amounts of olefin reactant. Further, a substantially stoichiometric excess of isoparaffins over that required to react with olefin is employed to insure contact of isoparaffins with olefins under alkylation reaction conditions. Further, as olefin reactants are generally substantially more soluble in acid catalysts than are isoparaffin reactants, high-shear mixing of the alkylation reaction mixture is generally provided sufficient to form emulsions of acid catalysts and hydrocarbon reactants. Formation of such emulsions increases the contact area between acid catalyst, containing dissolved olefins with isoparaffin hydrocarbons, thus materially improving yield and quality of alkylate product.
Commonly, where sulfuric acid is the selected acid catalyst, the alkylation reaction emulsion is one wherein isoparaffin hydrocarbon is emulsified in a continuous acid phase, although it is known to employ reaction emulsions comprising acid catalyst phase suspended in a continuous isoparaffin hydrocarbon phase. Alkylation reaction mixtures comprising about 40-70 volume percent sulfuric acid catalyst and about 60-30 volume percent hydrocarbon phase are known to form emulsions wherein the acid phase is continuous.
In the prior art, sulfuric and fluorosulfonic acids alone, and mixtures of the two comprising a major portion of fluorosulfonic acid, are known to be effective catalysts for the liquid phase alkylation of isoparaffin hydrocarbons with olefin hydrocarbons. Additionally, U.S. Pat. No. 2,313,013 claims that alkylation of an isoparaffin with an olefin hydrocarbon employing pure fluorosulfonic acid as catalyst is superior to alkylation employing sulfuric acid catalyst. In U.S. Pat. No. 3,231,633 it is taught that the catalytic activity of fluorosulfonic acid may be improved by the addition of a minor amount of H.sub.2 SO.sub.4 (e.g., not less than 50 weight percent HFSO.sub.3 in the catalyst) thereto. Also, In U.S. Pat. No. 2,425,572, it is disclosed that the catalytic activity of H.sub.2 SO.sub.4 may be substantially improved by the addition of about 1-10% of chlorosulfonic acid or other substituted sulfonic acids.
The sulfonic acids, such as fluorosulfonic and chlorosulfonic, are relatively expensive materials compared to sulfuric acid. In alkylation reactions, acid catalyst is consumed at rates ranging from about 0.1 up to 10 and more pounds of catalyst per gallon of alkylate product as a result of side reactions such as hydrolysis and reaction with olefin hydrocarbons. Consequently, the expense of providing sulfonic acids as the major components of alkylation catalysts may become prohibitively expensive in commercial alkylation processes. Both fluorosulfonic and chlorosulfonic acid are known to react with water thereby forming the respective hydrogen halide and H.sub.2 SO.sub.4. Consequently, alkylation processes employing catalysts comprising a major portion of such sulfonic acids must be kept substantially dry in order to prevent destruction of the acid.